1. Field of the Invention
My invention relates generally to the shift mechanism for an automotive vehicle transmission, and especially to a transaxle transmission mechanism wherein a common axis of the engine and transmission is transversely disposed with respect to the fore-and-aft axis of the vehicle.
2. Description of the Prior Art
The shift mechanism according to my invention operates to provide the shifting motion in a transaxle transmission having, in addition to the conventional forward speed ratios and a reverse speed ratio, a fifth or overdrive speed ratio. A gearshift mechanism for such a transmission must allow the conventional gearshift pattern for the lowest four forward speed ratios and the reverse gear ratio that has received general acceptance within the automotive industry. In addition, a fifth forward speed plane must be added to the conventional shift pattern adjacent the three-four shift plane and remote from the reverse shift plane. The transmission with which such a shift mechanism is designed to work includes a first shift rail on which two shift forks and a reverse pinion shift collar are mounted and a second shift rail on which a third shift fork is mounted for controlling the engagement of the fifth speed gears. Present-day transmissions are required to provide a positive interlock system, which assures that the shift cane controlled by the vehicle operator will engage the speed ratio selected by the operator. The interlock must positively prevent all other speed ratios from becoming accidentally engaged. Furthermore, the shift mechanism must provide means to prevent accidental disengagement of the selected gears from the driving connection.
Shifting mechanisms for controlling a four forward speed ratio transmission providing the interlocking capability are well known. U.S. Pat. Nos. 3,264,893; 3,962,930 and 4,174,644 describe shift mechanisms of this type. However, shifting mechanisms adapted to control a four speed transmission are not suitable for controlling the shifting motion required in a five speed transmission.
The movement of the shift selector shaft in a transaxle transmission can be transferred to a first shift rail so that the shift forks mounted on the rail are moved in response to the control motion applied to the shift selector shaft by the vehicle operator. Furthermore, it is known in the art that the first shift rail can be adapted to cause a reverse idler to engage selectively the reverse drive gears of the transmission in response to motion of the shift selector shaft. A shift interlock system can be readily adapted to block engagement of unselected speed ratios and to allow driving engagement only of the selected speed ratio by mounting an interlock collar and selector pin on this first shift rail.
However, when a second shift rail is required in a five speed transaxle transmission, the shifting movement of the shift selector shaft must be coordinated between two shift rails and the interlock system must be effective in blocking the motion of the unselected shift rail and of the unselected shift forks mounted on the selected shift rail.